Cyclopropylaklyl or -alkenyl or heterocyclic compounds, process for their preparation and their use in liquid-crystalline mixtures

ABSTRACT

Disclosed and claimed are liquid-crystalline cyclopropylalkyl or -alkenyl or heterocyclic compounds, process for their preparation, and their use in liquid-crystalline mixtures. The novel cyclopropylalkyl or -alkenyl or heterocyclic compounds are of the general formula ##STR1## In this formula A 1 , A 2  and A 3  are unsubstituted or substituted, aromatic or heteroaromatic molecular components such as 1,4-phenylene or pyrimidine-2,5-diyl which are linked via a single bond (in the case where k and m=0) or via functional groups M 1  and M 2 , such as CO--O or CH 2  --O; j, k, l, m and n are zero, 1 or 2. The radicals R 2 , R 3  and R 4  are H or alkyl/alkenyl, R 1  is alkyl/alkenyl or one of the substitutents known from LC chemistry such as an α-haloalkanoic acid radical. At least one of the components A 1 , A 2  and A 3  can be heteroaromatic, and G is alkylene or alkenylene.

RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.07/919,085, filed Jul. 23, 1992, now abandoned, which in turn is acontinuation of application Serial No. 07/799,754, filed Nov. 27, 1991,now abandoned, which in turn is a continuation of application Ser. No.07/522,248, filed May 11, 1990, now abandoned, with a claim of priorityfrom German application No. P3915804.7, filed May 13, 1989; each ofthese predecessor U.S. and priority German applications are herebyincorporated herein by reference. This application is also acontinuation-in-part of application Ser. No. 07/917,792, filed Jul. 20,1992, now abandoned, as a continuation of application Ser. No.07/804,618, filed Dec. 4, 1991, now abandoned, as a continuation ofapplication Ser. No. 07/560,017, filed Jul. 27, 1990, now abandoned, asa continuation of application Serial No. 07/275,210, filed Nov. 23,1988, now abandoned, with a claim of priority from German applicationNo. P3739884.9, filed Nov. 25, 1987; and, each of these predecessor U.S.and priority German applications are hereby incorporated herein byreference. This application claims the benefits of priority under 35U.S.C. §119 from German applications P3915804.7 and P3739884.9, filedrespectively on May 13, 1989 and Nov. 25, 1987.

FIELD OF THE INVENTION

The present invention relates to cyclopropylalkyl or -alkenyl orheterocyclic compounds, processes for their preparation and their use inliquid-crystalline mixtures.

BACKGROUND OF THE INVENTION

The unusual combination of anisotropic and fluid behaviour of liquidcrystals has resulted in their use in a large number of electro-opticalswitching and display devices. In these, their electrical, magnetic,elastic and/or thermal properties can be used for changes inorientation. Optical effects can then be achieved, for example, with theaid of birefringence, the inclusion of dichroically absorbing dyemolecules ("guest-host mode") or light scattering.

In order to satisfy the constantly increasing practical requirements inthe various fields of application, there is a constant demand for novel,improved liquid-crystal mixtures and thus also for a large number ofmesogenic compounds of a very wide variety of structures. This appliesboth to the areas in which nematic LC phases (for example TN="twistednematic", STN="supertwisted nematic", SBE="supertwisted birefringenceeffect", ECB="electrically controlled birefringence") are used, and inthose using smectic LC phases (for example ferroelectric andelectroclinic).

Many of the compounds which are suitable for LC mixtures can bedescribed by a structure principle (building plan) [see, for example J.Am. Chem. Soc. 108, 4736 (1986), structure I; Science 231, 350 (1986),FIG. 1A; J. Am. Chem. Soc. 108, 5210 (1986), FIG. 3] in which nuclei ofcyclic compounds--aromatics, heteroaromatics, but also saturated ringsystems--are linked to alkyl side chains which are straight-chain orsubstituted in the chain by small groups (for example methyl orchlorine) and are thus branched.

Compounds which contain a terminal cyclopropyl-substituted alkyl chainas a partial structural element are described, for example, in U.S.application Nos. 3,948,961, 3,966,969 and 4,014,922 (Henrick et al.).The compounds are said to be suitable as insecticides, but aliquid-crystalline behaviour is not reported. The compounds listed inthese publications differ from those defined below, in particularthrough the fact that they are always linked to the molecular radicalvia an ester function and in this molecular radical, although havingaromatic ring systems, do not contain any heteroaromatic ring systems.

EP-A 0,244,129 relates to 2,2-dimethylcyclopropane derivatives which areoptically active and are linked to one of the known mesogenic radicalsvia a --CO--O--CH₂ --, --O--CO-- or --CH₂ -- bridge (the cyclopropylring is located at the right-hand end of the particular bridgingmember). These compounds are said to be suitable as components forferroelectric LC mixtures (spontaneous polarization of up to 11 nC/cm²).

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to provide novel mesogeniccompounds which can be combined with many other components to form avery wide variety of LC mixtures. The compounds defined below achievethis object:

Liquid-crystalline cyclopropylalkyl or -alkenyl and/or heterocycliccompounds of the general formula (I) ##STR2## in which:

R¹ is straight-chain or branched (with or without an asymmetrical carbonatom) alkyl or alkenyl having 2 to 16 carbon atoms, it also beingpossible for one or two non-adjacent --Ch₂ -- groups to be replaced by--O--, --S--, --CO--, --CO--O--, --O--CO-- or --O--CO--O and it alsobeing possible for H to be replaced by F, or one of the followingradicals ##STR3## CN, OCF₃, OCF₂, F or CF₃ ; A¹, A², and A³ areidentical or different, unsubstituted or mono-or dihalo-substituted1,4-phenylene, unsubstituted or 1- or 4-CN-substituted1,4-cyclohexylene, trans-1,4-cyclohexene, pyrazine-2,5-diyl,pyridazine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, or(1,3,4)-thiadiazole-2,5-diyl;

M¹ and M² are identical or different CO--O, O--CO, CO--S, S--CO, CH₂--O, O--CH₂, C═C, CH₂ --CH₂ or a single bond;

G is a straight-chain or branched alkylene having 1 to 16 carbon atomsor alkenylene having 2 to 16 carbon atoms in which it is also possiblefor one or two non-adjacent --CH₂ -- groups to be replaced by --O--,--S--, --O--CO--, --CO--O--, --S--CO-- or --CO--S--;

R², R³ and R⁴ are H or straight-chain or branched alkyl having 1 to 16carbon atoms or alkenyl having 2 to 16 carbon atoms in which it is alsopossible for one --CH₂ -- group to be replaced by --O--, --CO--O-- or--O--CO--;

k and m are zero or 1; and

j, l and n are zero, 1 or 2.

In some instances it is preferred that: a) j+l+n=2 or 3; and/or b) oneof the groups A¹, A² and A³ is not 1,4-phenylene ortrans-1,4-cyclohexylene; and/or c), in the case where R² =H, R³ and R⁴need not simultaneously be CH₃ and G need not be CO--O--CH₂, O--CO orOCH₂, more preferably R³ and R⁴ are not simultaneously CH₃.

DETAILED DESCRIPTION

Preferred compounds of this type are those in which, in the generalformula (I), the (--A¹)_(j) (--M¹)_(k) (--A²)_(l) (--M²)_(m) (--A³)_(n)-- group denotes: ##STR4## In addition, particularly preferred compoundsare those in which, in the general formula (I) , the group R¹ (--A¹)_(j)(--M¹)_(k) (--A²)₁ (--M²)_(m) (--A³)_(n) is: ##STR5## Particularlypreferred compounds of the general formula (I) are also those in whichA¹, A² and A³ are identical or different, unsubstituted 1,4-phenylene,mono- or di-fluoro-substituted, 1,4-phenylene, 1,4-cyclohexylene,pyridine-2,5-diyl or pyrimidine-2,5-diyl.

The novel cyclopropylalkyl or -alkenyl compounds are chemically,photochemically and thermally stable and have good mixturecompatibility. Compared with the corresponding n-alkyl homologs, thesecompounds frequently have a lower melting point; in mixtures such as LCmixtures frequently result in lower melting points; and, a lower valuefor the optical anisotropy Δn.

A further solution of the said object is a liquid-crystal mixturecontaining at least one liquid-crystalline compound and containing, asthe liquid-crystalline compound, at least one compound of the generalformula (I).

The liquid-crystal mixtures comprise 2 to 20, preferably 2 to 15,components, including at least one of the compounds according to theinvention. The other components are preferably selected from knowncompounds having nematic, cholesteric and/or tilted smectic phases,including, for example, Schiff bases, biphenyls, terphenyls,phenylcyclohexanes, cyclohexylbiphenyls, pyrimidines, cinnamic acidesters, cholesterol esters and various bridged, polynuclearp-alkylbenzoic acid esters with terminal polar groups. In general,commercially available liquid-crystal mixtures exist, even beforeaddition of the compound(s) according to the invention, as mixtures of avery wide variety of components of which at least one is mesogenic,i.e., exhibits a liquid crystal phase [=at least one enantiotropic(clear point>melting point) or monotropic (clear point<melting point)mesophase formation can be expected] as the compound, in derivatizedform or mixed with certain cocomponents.

The liquid-crystal mixtures generally contain 0.01 to 70% by weight, inparticular 0.05 to 50% by weight, of the compound(s) according to theinvention.

The compounds according to the invention can be prepared by standardreactions known per se from mesogenic monofunctional reactive parentstructures by linking with likewise monofunctional reactivecyclopropylalkyl compounds, where the synthesis of the two componentsmay be regarded as known.

Thus, for example, mesogenic hydroxyl or mercapto compounds can belinked to cyclopropyl-alkanols in the presence oftriphenylphosphine/azodicarboxylic acid diesters (Mitsunobu reaction,for example in J. Chem. Soc. Perkin Trans. 1975, 461). It is alsopossible to react the alkali metal salts or alkaline earth metal saltsof these mesogenic hydroxyl or mercapto compounds, produced separatelyor intermediately, with halo-, toluenesulfonyloxy- ormethylsulfonyloxy-cyclopropylalkyl compounds (Williamson reaction, forexample in Patai, The Chemistry of the Ether Linkage, IntersciencePublishers, N.Y. 1967, pp. 446-468).

However, it is also possible to react mesogenic carboxylic acids withcyclopropylalkanols under condensation conditions (for example in March,Advanced Organic Chemistry, 2nd Ed., McGraw-Hill, Kogakuska Ltd., Tokyo1977, pp. 363-365. This is also possible in the same way using mesogenichydroxyl or mercapto compounds and cyclopropyl-alkanoic acids.

The cyclopropylalkyl compounds necessary for the linkage are prepared bystandard methods; in this respect, reference is made to theabovementioned publications (US-A) by Henrick et al.

In addition, cyclopropyl compounds can be prepared by the Simmons-Smithreaction (see, for example, in March, Advanced Organic Chemistry, pp.793-794) from the corresponding olefins.

The following non-limiting Examples are given by way of illustrationonly and are not to be considered a limitation of this invention.

EXAMPLES

In the Examples below, parts by weight have the same relationship toparts by volume as the kilogram to the liter.

EXAMPLE 1 5-Heptyloxy-2-[4-(9-cyclopropyl-nonyl)oxy-phenyl]-pyrimidine##STR6## 0.5 part by weight of 9-cyclopropylnonanol and 0.95 part byweight of 4-(5-heptyloxypyrimidine-2-yl)-phenol were added to a solutionof 0.52 part by volume of diethyl azodicarboxylate and 0.85 part byweight of triphenylphosphine. After a reaction time of 24 hours, thesolvent was removed by distillation and the residue was purifiedchromatographically (SiO₂ /CH₂ Cl₂). After recrystallization from2-propanol, 0.52 part by weight of colorless crystals were obtained.

Phase sequence: C 56.4 S_(c) 71.3 S_(A) 83.4 N 85.1 I

The syntheses below were carried out in accordance with the procedure ofExample 1, adjusting the quantities appropriately.

EXAMPLE 2 5-Hexyl-2-[4-(9-cyclopropyl-nonyl)oxy-phenyl]pyrimidine##STR7## Phase sequence: C 44 N 53 I EXAMPLE 3 5-Octyl-2 -[4-(9-cyclopropyl-nonyl)oxy-phenyl]pyrimidine ##STR8## Phase sequence: C41.3 S_(c) 51 S_(A) 57.6 N 60.2 I n∥1.616 n⊥1.486 Δn=0.13 (at 45° C.,589 nm)

Measurement method: An important characteristic quantity for the qualityof the contrast of a LC display is the optical birefringence Δn=n∥-n⊥.n∥ and n⊥ are the refractive indices for light polarized parallel orperpendicular to the director n. Both refractive indices can bedetermined as a function of temperature and wavelength using an Abberefractometer.

EXAMPLE 4 5-Octyloxy-2-[4-(9-cyclopropyl-nonyl)oxy-phenyl]pyrimidine##STR9## Phase sequence: C 69.2 S_(c) 75.8 S_(A) 90.2 I EXAMPLE 55-Nonyl-2-[4-(9-cyclopropyl-nonyl) oxy-phenyl]pyrimidine ##STR10## Phasesequence: C 52.8 S_(c) 56.8 S_(A) 67.2 I EXAMPLE 65-Decyl-2-[4-(9-cyclopropyl-nonyl)oxy-phenyl]pyrimidine ##STR11## Phasesequence: C 44 S_(c) 64.9 S_(A) 67.7 I EXAMPLE 75-Undecyl-2-[4-(9-cyclopropyl-nonyl)oxy-phenyl]-pyrimidine ##STR12##Phase sequence: C 48 S_(c) 70.2 S_(A) 71.8 I EXAMPLE 85-Undecyloxy-2-[4-(9-cyclopropyl-nonyl)oxy-phenyl]-pyrimidine ##STR13##Phase sequence: C 68 S_(c) 95 I EXAMPLE 95-Dodecyl-2-[4-(9-cyclopropyl-nonyl)oxy-phenyl]pyrimidine ##STR14##Phase sequence: C 52 S_(c) 72.3 I EXAMPLE 10 2 -Decylthio-5-[4-(9-cyclopropyl-nonyl)oxy-phenyl]pyrimidine ##STR15## Phase sequence:C 67.5 [38 S₂ 57 S_(c) 65] I EXAMPLE 115-(9-Cyclopropyl-nonyl)oxy-2-(4-heptyloxy-phenyl)pyrimidine ##STR16##Phase sequence: C 64.7 S_(c) 91 I EXAMPLE 125-(9-Cyclopropyl-nonyl)oxy-2-(4-octyloxy-phenyl)-pyrimidine ##STR17##Phase sequence: C 63.7 S_(c) 93.2 I EXAMPLE 135-Octyl-2-[4-<5-((3S)-2,2-dimethylcyclopropyl)-3methylpentyl>oxy-phenyl]pyrimidine##STR18## Phase sequence: C[-21.5 S_(A) 16]18.5 I [α]²⁵ _(D) : -5.2(c=5, CH₂ Cl₂)

Measurement method: If a small amount of a chiral compound is added to a(non-chiral) solvent, the plane of linear-polarized light is rotated bythe (characteristic) angle α; this angle is given as follows [α]^(T)_(D) (C=x, solv.), where the symbols have the following meaning:x=concentration of the solution in g/l, solv.=solvent, D=589 nm (NaDline), T=temperature of the solution. The angle of rotation isdetermined in a polarimeter at a path length of 10 cm.

EXAMPLE 14(2S,3S)-4-[5-(9-cyclopropyl-nonyl)oxy-pyrimidine-2-yl)-phenyl-2-chloro-3-methyl-pentanoate ##STR19## Phase sequence: C [38 S_(c) 40S_(A) 44.3] 48.5 I [α]²⁵ _(D) =-2.0 (c=4, CH₂ Cl₂) EXAMPLE 155-Octyl-2-[4-(6-cyclopropyl-hexyl)oxy-phenyl]pyrimidine ##STR20## Phasesequence: C 39 S_(c) 46 S_(A) 50 N 59.5 I EXAMPLE 16 5-Decyl-2-[4-(6-cyclopropyl-hexyl)oxy-phenyl]pyrimidine ##STR21## Phase sequence:C 42 S_(c) 60 S_(A) 65 I EXAMPLE 175-Heptyloxy-2-[4-(6-cyclopropyl-hexyl)oxy-phenyl]pyrimidine ##STR22##Phase sequence: C 54 S_(c) 72 S_(A) 78 N 88 I EXAMPLE 185-Octyloxy-2-[4-(6-cyclopropyl-hexyl)oxy-phenyl]pyrimidine ##STR23## hasan S_(c) /S_(A) transition at 81, an S_(A) /N transition at 89 and aclear point at 92° C. EXAMPLE 195-(6-Cyclopropyl-hexyl)oxy-2-(4-nonyloxy-phenyl)pyrimidine ##STR24##Phase sequence: C 56.5 S_(c) 79 S_(A) 85 N 89.5 I EXAMPLE 205-(6-Cyclopropyl-hexyl)oxy-2-(4-undecyloxy-phenyl)pyrimidine ##STR25##Phase sequence: C 57.5 S_(c) 76.5 S_(A) 86.7 N 87 I EXAMPLE 215-(6-Cyclopropyl-hexyl)oxy-2-(4-dodecyloxy-phenyl)pyrimidine ##STR26##Phase sequence: C 61 S_(c) 77 S_(A) 87 I EXAMPLE 22trans-2-<9-[4-(5-octyl-pyrimidin-2-yl)phenyloxy]nonyl>-cyclopropaneethylcarboxylate##STR27## Phase sequence: C [11 S_(c) 36 S_(A]) 38 I EXAMPLE 235-Octyl-2-[4-(7-cyclopropyl-heptyl)oxy-phenyl]pyrimidine ##STR28## Phasesequence: C 33 S_(c) 45.5 S_(A) 54.6 N 58.4 I EXAMPLE 245-(7-Cyclopropyl-heptyl)oxy-2-(4-nonyloxy-phenyl)pyrimidine ##STR29##Phase sequence: C 60 S_(c) 87.9 S_(A) 90.4 I EXAMPLE 255-(7-Cyclopropyl-heptyl)oxy-2-(4-undecyloxy-phenyl)pyrimidine ##STR30##Phase sequence: C 53.4 S_(c) 87.6 S_(A) 90.5 I EXAMPLE 265-(7-Cyclopropyl-heptyl)oxy-2-(4-dodecyloxy-phenyl)pyrimidine ##STR31##Phase sequence: C 67.4 S_(c) 88.1 S_(A) 90.5 I EXAMPLE 275-Octyloxy-2-[4-(7-cyclopropyl-heptyl)oxy-phenyl]pyrimidine ##STR32##Phase sequence: C 60 S_(c) 78.2 S_(A) 90 N 90.2 I EXAMPLE 282-Octylthio-5-[4-(7-cyclopropyl-heptyl)oxy-phenyl]pyrimidine ##STR33##Phase sequence: C [41 S₃ 42 S_(c) 55.5] 61.6 S_(A) 62.2 I EXAMPLE 295-Octyl-2-[4-(11-cyclopropyl-5-oxa-undecyl)oxy-phenyl]pyrimidine##STR34## Phase sequence: C [16 S_(c) 25.6 N 31] 40.9 I EXAMPLE 305-(9-Cyclopropyl-nonyl)oxy-2-[4-(trans-4-pentyl-cyclo-hexyl)-carbonyloxy-phenyl]pyrimidine ##STR35## Phase sequence: C [76 S₂ 84.3]86.5 S_(c) 129.2 N 179 I EXAMPLE 315-(6-Cyclopropyl-5-oxa-hexyl)oxy-2-(4-nonyloxy-phenyl)pyrimidine##STR36## Phase sequence: C [58 S_(c) 58.4 N 72] 72.4 I EXAMPLE 325-Octyl-2-[4-(6-cyclopropyl-5-oxa-hexyl)oxy-phenyl]pyrimidine ##STR37##Phase sequence: C [-4 S_(c) 22] 28.5 N 40.2 I EXAMPLE 335-(9-Cyclopropyl-nonyl)oxy-2-(4-undecyloxy-phenyl)pyrimidine ##STR38##Phase sequence: C 55 S_(c) 94.2 I EXAMPLE 345-(9-Cyclopropyl-nonyl)oxy-2-(4-dodecyloxy-phenyl)pyrimidine ##STR39##Phase sequence: C 63 S_(c) 94.2 I EXAMPLE 355-Decyl-2-[4-(7-cyclopropyl-heptyl)oxy-phenyl]pyrimidine ##STR40## Phasesequence: C 40.3 S_(c) 61 S_(A) 66.2 I EXAMPLE 365-(7-Cyclopropyl-heptyl)oxy-2-(4-octyloxy-phenyl)pyrimidine ##STR41##Phase sequence: C 56.5 S_(c) 89.1 S_(A) 91.6 I EXAMPLE 375-Dodecyl-2-[4-(11-cyclopropyl-undecyl)oxy-phenyl]pyrimidine ##STR42##Phase sequence: C 72 S_(c) 95.3 I EXAMPLE 385-Decyl-2-[4-(11-cyclopropyl-undecyl)oxy-phenyl]pyrimidine ##STR43##Phase sequence: C 51.7 S_(c) 65.6 S_(A) 67.3 I EXAMPLE 39 5-(7-Cyclopropyl-heptyl) oxy-2-(4-hexyloxy-phenyl)pyrimidine ##STR44##Phase sequence: C 51.8 S_(c) 86.5 S_(A) 89.6 N 89.8 I EXAMPLE 405-Octyl-2-[4(8-cyclopropyl-octyl)oxy-phenyl]pyrimidine ##STR45## Phasesequence: C 35 S_(c) 51.5 S_(A) 55.5 N 61.2 I EXAMPLE 41 5-(8-Cyclopropyl-octyl)oxy-2-(4-nonyloxyphenyl)pyrimidine ##STR46## Phasesequence: C 56.2 S_(c) 91.8 S_(A) 93 I EXAMPLE 425-(8-Cyclopropyl-octyl)oxy-2-(4-undecyloxy-phenyl)pyrimidine ##STR47##Phase sequence: C 53.6, S_(c) 92.3 S_(A) 93.1 I EXAMPLE 435-(8-Cyclopropyl-octyl)oxy-2-(4-dodecyloxy-phenyl)pyrimidine ##STR48##Phase sequence: C 54.9 S_(c) 92.3 S_(A) 93 I EXAMPLE 445-Octyloxy-2-[4-(8-cyclopropyl-octyl)oxy-phenyl]pyrimidine ##STR49##Phase sequence: C 51 S_(c) 79.2 S_(A) 91 N 91.6 I EXAMPLE 452-Octylthio-5-[4-(8-cyclopropyl-octyl)oxy-phenyl]pyrimidine ##STR50##Phase sequence: C [42.2 S_(c) 59.5 S_(A) 62.5] 64.7 I EXAMPLE 465-(8-Cyclopropyl-octyl)oxy-2-(4-hexyloxy-phenyl)pyrimidine ##STR51##Phase sequence: C 54.1 S_(c) 88.2 S_(A) 90.8 I EXAMPLE 475-(8-Cyclopropyl-octyl)oxy-2-(4-oxtyloxy-phenyl)pyrimidine ##STR52##Phase sequence: C 56.4 S_(c) 91.7 S_(A) 92.9 I EXAMPLE 485-(11-Cyclopropyl-undecyl)oxy-2-(4-dodecyloxy-phenyl)pyrimidine##STR53## Phase sequence: 54.6 S_(c) 73.8 I EXAMPLE 493-(9-Cyclopropyl-nonyl)oxy-6-(4-octyloxy-phenyl)pyridazine ##STR54##Phase sequence: C [82 S_(c) 95.7] 100 I EXAMPLE 505-Decyl-2-[4-(8-cyclopropyl-octyl)oxy-phenyl]pyrimidine ##STR55## Phasesequence: C 42.3 S_(c) 62.5 S_(A) 67.2 I EXAMPLE 515-Octyloxy-2-[4-(cyclopropylmethyl)oxy-phenyl]pyrimidine ##STR56## Phasesequence: C 59 S_(c) 62.8 S_(A) 72.9 N 73.6 I EXAMPLE 522-(9-Cyclopropyl-nonyl)oxy-5-[4-(9-cyclopropyl-nonyl-oxy)phenyl]pyrimidine##STR57## Phase sequence: C [79.3 S_(c) 79.5] 89.4 I EXAMPLE 532-(9-Cyclopropyl-nonyl)oxy-5-(4-decyloxyphenyl)pyrimidine ##STR58##Phase sequence: C [70 S₃ 70.55 S_(c) 84 S_(A) 87.6] 88 I EXAMPLE 544-(2-Octylthiopyrimidin-5-yl)phenyltrans-2-hexyl-cyclopropanecarboxylate ##STR59## Phase sequence: C 40.5 IEXAMPLE 55 5-(8-Cyclopropyl-octyl)oxy-2-(4-decyloxy-phenyl)pyrimidine##STR60## Phase sequence: C 58.5 S_(c) 91.6 S_(A) 92 I EXAMPLE 565-(8-Cyclopropyl-octyl)oxy-2- [4-butyloxy-phenyl]pyrimidine ##STR61##Phase sequence: C 55.4 S_(c) 81 S_(A) 87.8 I EXAMPLE 57(R)-4-[2-(9-Cyclopropyl-nonyl)oxy-pyrimidin-5-yl]-phenyl2,2-dimethyl-1,3-dioxolane-4-carboxylate ##STR62## Phase sequence: C 84I [α]²⁰ _(D) : +5.46 (C=2, CH₂ Cl₂) EXAMPLE 58 (2S,3S)-4-[2-(9-Cyclopropyl-nonyl) oxy-pyrimidin-5-yl]-phenyl2-chloro-3-methyl-pentanoate ##STR63## Phase sequence: C 81 I [α]²⁰ _(D): +1.2 (C=2, CH₂ Cl₂) EXAMPLE 595-Octyl-2-[4-(4-cyclopropyl-butyl)oxy-phenyl]pyrimidine ##STR64## Phasesequence: C [16 S_(c) 37 S_(A) 43.6] 45 N 56 I EXAMPLE 605-Decyl-2-[4-cyclopropyl-butyl)oxy-phenyl]pyrimidine ##STR65## Phasesequence: C [47 S_(c) 48] 64 N 88 I EXAMPLE 615-(4-Cyclopropyl-butyl)oxy-2-(4-hexyloxy-phenyl)pyrimidine ##STR66##Phase sequence: C [47 S_(c) 48] 64 N 88 I EXAMPLE 625-Octyl-2-[4-(5-cyclopropyl-pentyl)oxy-phenyl]pyrimidine ##STR67## Phasesequence: C [18 S_(c) 34] 38 S_(A) 51 N 54 I EXAMPLE 635-Decyl-2-[4-(5-cyclopropyl-pentyl)oxy-phenyl]pyrimidine ##STR68## Phasesequence: C 48 S_(c) 53 S_(A) 62 I EXAMPLE 645-(5-Cyclopropyl-pentyl)oxy-2-(4-hexyloxy-phenyl)pyrimidine ##STR69##Phase sequence: C 53 S_(c) 73 S_(A) 75 N 86 I EXAMPLE 655-(7-Cyclopropyl-heptyl)oxy-2-(4-decyloxy-phenyl)pyrimidine ##STR70##Phase sequence: C 55.7 S_(c) 90 S_(A) 92.5 I EXAMPLE 664-(5-Octyl-pyrimidin-2-yl)phenyl trans-2-hexyl-cyclo-propylcarboxylate##STR71## Phase sequence: C 44 I EXAMPLE 67 4-[2-(9-cyclopropylnonyl)oxy-pyrimidin-5-yl]phenyl(2R,3R)-3-propyl-oxirane-2-carboxylate ##STR72## Phase sequence: C 75 I[α]²⁰ _(D) : -9.6 (C=2, CH₂ Cl₂) EXAMPLE 684-[2-(9-Cyclopropylnonyloxy)-pyrimidin-5-yl]phenyl(2S)-2-fluoro-3-methyl-butanoate ##STR73## Phase sequence: X [63 S_(A)64] 78 I [α]²⁰ _(D) : -1.0 (C=2, CH₂ Cl₂) EXAMPLE 692-(4-Hexyloxy-phenyl)-5-[4-(6-cyclopropyl-hexyloxy)-phenyl]pyrimidine##STR74## Phase sequence: X [77 S₄ 103]110 S₃ 129 S_(c) 189 S_(A) 198 IEXAMPLE 705-(4-Cyclopropyl-butyloxy)-2-[4-(5-oxa-nonyloxy)phenyl]pyrimidine##STR75## Phase sequence: C 42 S_(c) 45 S_(A) 47 N 64 I EXAMPLE 715-(5-Cyclopropyl-pentyloxy)-2-[4-(5-oxa-nonyloxy)phenyl]pyrimidine##STR76## Phase sequence: X 39 S_(c) 63 S_(A) 65 N 67 I EXAMPLE 725-(6-Cyclopropyl-hexyloxy)-2-[4-(5-oxa-nonyloxy)phenyl]pyrimidine##STR77## Phase sequence: X 46 S_(c) 66 S_(A) 67 N 69 I EXAMPLE 735-(7-Cyclopropyl-heptyloxy)-2-[4-(5-oxa-nonyloxy)phenyl]pyrimidine##STR78## Phase sequence: C 43 S_(c) 73 I EXAMPLE 745-Cyclopropylmethyloxy-2-(4-octyloxyphenyl)pyrimidine ##STR79## Phasesequence: C 63 N 64 I EXAMPLE 755-Octyl-2-[4-(6-cyclopropyl-hexyloxy)phenyl]pyrimidine ##STR80## Phasesequence: C 37 S_(c) 46 S_(A) 50 N 59 I EXAMPLE 765-Octyloxy-2-[4-(6-cyclopropyl-hexyloxy)phenyl ]pyrimidine ##STR81##Phase sequence: C 56 S_(c) 80 S_(A) 88 N 91 I EXAMPLE 775-(6-Cyclopropyl-hexyloxy)-2-(4-octyloxyphenyl)pyrimidine ##STR82##Phase sequence: C 56 S_(c) 78 S_(A) 84 N 89 I EXAMPLE 782-[4-(7-Cyclopropyl-heptyloxy)phenyl]-5-octyl-pyridine ##STR83## Phasesequence: C 49 S₂ 63 S_(c) 72 I EXAMPLE 792-[4-(11-Cyclopropyl-undecyloxy)phenyl]-5-octyl-pyridine ##STR84## Phasesequence: C 57 S₂ 63 S_(c) 72 I EXAMPLE 802-(trans-4-Pentyl-cyclohexyl)-5-[4-(11-cyclopropyl-undecyloxy)phenyl]-1,3,4-thiadiazole##STR85## Phase sequence: C 111 S_(c) 113 S_(A) 156 N 157 I EXAMPLE 814-(5-Octyl-pyrimidin-2-yl)phenyl 7-cyclopropyl-heptanoate ##STR86##Phase sequence: C [36 S_(c) 40.5 S_(A) 44 N 46] 51 I EXAMPLE 824-(5-Decyl-pyrimidin-2-yl)phenyl 7-cyclopropyl-heptanoate ##STR87##Phase sequence: C 48 S_(c) 57 I EXAMPLE 834-(5-Octyloxy-pyrimidin-2-yl)phenyl 7-cyclopropyl-heptanoate ##STR88##Phase sequence: C 62 S_(c) 77 S_(A) 84 N 84.3 I EXAMPLE 84

A mixture comprising 55 mol-%of the compound of Example 6 and 45 mol-%ofthe compound of Example 3 exhibited the phase sequence C 31 S_(c) 58S_(A) 64 I.

EXAMPLE 85

A mixture comprising 67 mol-% of the compound of Example 6 and 33 mol-%of the compound of Example 11 exhibited the phase sequence C 35 S_(c) 74S_(A) 78 I.

EXAMPLE 86

A mixture comprising 20 mol-% of the compound of Example 6, 25.15 mol-%of (the mixture components, each of which is known)5-octyloxy-2-(4-decyloxy-phenyl)-pyrimidine, 11 mol-% of4-octyloxy-2-(4-octyloxy-phenyl)pyrimidine, 20 mol-% of 5-octyloxy-2-(4-hexyloxy-phenyl)pyrimidine and 23.85 mol-% of 5-octyloxy-2-(4-butyloxy-phenyl)pyrimidine exhibited the phase sequence C11.5 S_(c) 72 S_(A) 88 N 90 I.

EXAMPLE 87

A mixture comprising 60 mol-% of the compound of Example 56 and 40 mol-%of the compound of Example 55 exhibited the phase sequence C 34 S_(c) 82S_(A) 90 I.

EXAMPLE 88

A mixture comprising 62 mol-% of the compound of Example 43 and 38 mol-%of the compound of Example 37 exhibited the phase sequence C 48 S_(c) 93I.

EXAMPLE 89

A mixture comprising 57 mol-% of the compound of Example 43 and 43 mol-%of the compound of Example 65 exhibited the phase sequence C 36 S_(c) 90S_(A) 92 I.

EXAMPLE 90

A mixture comprising 60 mol-% of the compound of Example 27 and 40 mol-%of the compound of Example 47 exhibited the phase sequence C 33 S_(c) 85S_(A) 91 I.

EXAMPLE 91

A mixture comprising 45 mol-% of the compound of Example 24 and 55 mol-%of the compound of Example 71 exhibited the phase sequence C 25 S_(c) 70S_(A) 77 N 79 I.

EXAMPLE 92

A mixture comprising 30 mol-% of the compound of Example 65 and 70 mol-%of the compound of Example 71 exhibited the phase sequence C 25 S_(c) 70S_(A) 73 N 75 I.

EXAMPLE 93

A mixture comprising 40 mol-% of the compound of Example 76 and 60 mol-%of the compound of Example 56 exhibited the phase sequence C 35 S_(c) 81S_(A) 90 I.

EXAMPLE 94

A mixture comprising 65 mol-% of the compound of Example 71 and 35 mol-%of the compound of Example 56 exhibited the phase sequence C 17 S_(c) 69S_(A) 73 N 74 I.

Compared with a comparison mixture (binary mixture containing compoundsof comparable chain lengths without a cyclopropyl radical) comprising 40mol-% of 5-octyloxy-2-(4- octyloxy-phenyl)pyrimidine and 60 mol-% of5-octyloxy-2-(4- hexyloxy-phenyl)pyrimidine which had the phase sequenceC 39 S_(c) 90 S_(A) 98 N 100 I, Examples 93 and 94 had both a lowermelting point and a greater melting point depression.

EXAMPLE 95

A mixture comprising 50 mol-% of5-dodecyloxy-2-(4octyloxyphenyl)pyrimidine and 50 mol-% of the compoundof Example 24 had the phase sequence C 33 S_(c) 96 I. Compared with thecomparison mixtures (binary mixtures of comparable chain lengths withouta cyclopropyl radical) comprising 39 mol-% of 5-decyloxy-2-(4-octyloxy-phenyl)pyrimidine and 61 mol-% of5-octyloxy-2-(4-decyloxyphenyl)pyrimidine which had the phase sequence C39 S_(c) 94 S_(A) 100 I or comprising 60 mol-% of5-octyloxy-2-(4-decyloxyphenyl)pyrimidine and 40 mol-% of5-octyloxy-2-(4-dodecyloxyphenyl)pyrimidine which had the phase sequenceC 40 S_(c) 86 S_(A) 97 I, the mixture according to the invention hasboth a lower melting point and a greater melting point depression.

EXAMPLE 96

A mixture comprising:

30 mol-% of 5-octyloxy-2-(4-ethyloxy-phenyl)pyrimidine 6 mol-% of5-dodecyloxy-2-(4-butyloxy-phenyl)pyrimidine 15 mol-% of the compound ofExample 24 19 mol-% of the compound of Example 71 20 mol-% of thecompound of Example 56 10 mol-% of the compound of Example 43 had thephase sequence C 8 S_(c) 68 S_(A) 85 N 87.

EXAMPLE 97

A ferroelectric multicomponent mixture containing 10 mol-% of thecompound of Example 62 in .sup.(R) Felix 001*) had the phase sequence C-5 S_(c) 72 S_(A) *78 N* 93 I.

*) (C. Escher, H. R. Dubal, W. Hemmerling, I. Muller, D. Ohlendorf andR. Wingen, presented at "1st International Symposium on FerroelectricLiquid Crystals, Arcachon, BOrdeaux-France, Sep. 21-23, 1987",commercially available mixture from Hoechst Aktiengesellschaft havingthe phase sequence C-7 S_(c) *79 S_(A) * 83 N* 99 I)

The mixture can readily be oriented by conventional methods and isbistable. At 25° C., the mixture exhibited a spontaneous polarization of-5.8 nC/cm² and had the following switching times:

τ0-90=212 μs

τ10-90=90 μs

The viscosity of the mixture was 65 mPas and the double effective tiltangle was 18°.

EXAMPLE 98

A ferroelectric mixture comprising:

85.5 mol-% of the mixture from Example 96, 9.5 mol-% of4-(5-decyl-pyrimidin-2-yl)phenyl trans-4-pentyl-cyclohexanecarboxylateand 5 mol-% of 4-[2-((S)-7-methyl-nonyloxy)pyrimidin-5-yl]-phenyl (2S,3S)-2-chloro-3-methyl-pentanoate had the phase sequence C 5 S_(c) * 72S_(A) * 83 N* 88 I.

The mixture can readily be oriented by conventional methods and isbistable. At 25° C., the mixture exhibited a spontaneous polarization of-8.2 nC/cm² and had the following switching times:

τ0-90=139 μs

τ10-90=66 μs

The viscosity of the mixture was 280 mPas and the double effective tiltangle was 17°.

EXAMPLE 99 ##STR89## 4-(5-octylpyrimidin-2-yl)phenyl4-(6-cyclopropyl-hexyloxy)-2,3-difluorobenzoate

Preparation of 4-(6-cyclopropylhexyloxy)-2,3-difluoro-benzoic acid:

3.9 g of NaH (60% in oil) and 20 g of 6-cyclopropyl-hexanol were addedto a solution of 8.5 g of difluoro-phenol in 100 ml of DMF. After areaction time of 24 hours at room temperature, the solution was pouredonto ice and extracted with CH₂ Cl₂. After drying (Na₂ SO₄) and removalof the solvent by distillation, 16.5 g of6-cyclopropylhexyloxy-2,3-difluorobenzene were obtained as a colorlessoil.

30 ml of butyllithium (1.6M in hexane) were added dropwise at -60° C. toa solution of 11.7 g of 6-cyclopropylhexyloxy-2,3-difluorobenzene in 70ml of THF. After 5 hours at -60° C., CO₂ was passed in until saturationwas complete. The solution was warmed to RT, the solvent was removed bydistillation, 400 ml of H₂ O were added, and the mixture was acidifiedto pH 3 using acetic acid. The precipitate was filtered off withsuction. 12.3 g of 4-(6-cyclopropylhexyloxy)-2,3-difluorobenzoic acidwere obtained. Melting point 100°-108° C.

The following were obtained analogously:

4-(4-cyclopropylbutyloxy)-2,3-difluorobenzoic acid

4-(8-cyclopropyloctyloxy)-2,3-difluorobenzoic acid

1.2 g of 4-(6-cyclopropylhexyloxy)-2,3-difluorobenzoic acid were addedto a solution of 0.84 g of dicyclohexyl-carbodiimide, 50 mg ofdimethylaminopyridine and 1.15 g of 4-(5-octylpyrimidin-2-yl)phenol in50 ml of methylene chloride. After a reaction time of 24 hours, theprecipitate (dicyclohexylurea) was filtered off with suction. Thefiltrate was freed from solvent and chromatographed (SiO₂, CH₂ Cl₂).

Recrystallization from hexane gave 1.1 g of4-(5-octyl-pyrimidin-2-yl)phenyl4-(6-cyclopropylhexyloxy)-2,3-difluorobenzoate. ##STR90## The followingwere obtained analogously:

EXAMPLE 100 ##STR91## 4-(5-octyloxypyrimidin-2-yl)phenyl4-(6-cyclopropylhexyloxy)-2,3-difluorobenzoate ##STR92## EXAMPLE 101##STR93## 4-(5-dodecylpyrimidin-2-yl)phenyl4-(6-cyclopropyl-hexyloxy)-2,3-difluorobenzoate ##STR94## EXAMPLE 102##STR95## 4-(2-octyloxypyrimidin-5-yl)phenyl4-(6-cyclopropyl-hexyloxy)-2,3-difluorobenzoate ##STR96## EXAMPLE 103##STR97## 2-(4-octyloxyphenyl)pyrimidin-5-yl4-(6-cyclopropyl-hexyloxy)-2,3-difluorobenzoate ##STR98## EXAMPLE 104##STR99## 2-(4-dodecyloxyphenyl)pyrimidin-5-yl4-(6-cyclopropyl-hexyloxy)-2,3-difluorobenzoate ##STR100## EXAMPLE 105##STR101## 2-(4-octyloxyphenyl)pyrimidin-5-yl4-(6-cyclopropyl-hexyloxy)-2,3-difluorobenzoate ##STR102## EXAMPLE 106##STR103## (4-octyloxy)phenyl4-(6-cyclopropylhexyloxy)-2,3-difluorobenzoate ##STR104## Comparisonexample ##STR105## (4-octyloxy)phenyl 4-octyloxy-2,3-difluorobenzoate##STR106##

Comparison of the substance from Example 106 according to the inventionwith the compound mentioned shows that the compound according to theinvention had a lower melting point.

Replacement of the ethyl group by a cyclopropyl group reduced themelting point by about 1 degree.

EXAMPLE 107 ##STR107## 4-(5-octylpyrimidin-2-yl)phenyl4-(6-cyclopropyl-hexyloxy)-2,3-difluorobenzoate ##STR108## EXAMPLE 108##STR109## 4-(5-octyloxypyrimidin-2-yl)phenyl4-(6-cyclopropyl-hexyloxy)-2,3-difluorobenzoate ##STR110## EXAMPLE 109##STR111## 4-(5-octyloxyphenyl)pyrimidin-5-yl4-(8-cyclopropyl-octyloxy)-2,3-difluorobenzoate ##STR112## EXAMPLE 110##STR113## 4-(5-dodecylpyrimidin-2-yl)phenyl4-(8-cyclopropyl-octyloxy)-2,3-difluorobenzoate ##STR114## EXAMPLE 111##STR115## 4-(2-octyloxypyrimidin-5-yl)phenyl4-(8-cyclopropyl-octyloxy)-2,3-difluorobenzoate ##STR116## EXAMPLE 112##STR117## 4-(2-octylthiopyrimidin-5-yl)phenyl4-(8-cyclopropyl-octyloxy)-2,3-difluorobenzoate ##STR118## EXAMPLE 113##STR119## (4-octyloxy)phenyl4-(8-cyclopropyloctyloxy)-2,3-difluorobenzoate ##STR120## ComparisonExample ##STR121## (4-decyloxy)phenyl 4-octyloxy-2,3-difluorobenzoate##STR122## The compound from Example 113 according to the invention hada melting point which was lower by about 5 degrees than that of thecomparison compound. Replacement of an ethyl group by a cyclopropylgroup resulted in this lowering of the melting point which is favorablefor practical applications. EXAMPLE 114 ##STR123##4-(4-octyloxybenzoyloxy)phenyl4-(8-cyclopropyloctyloxy)-2,3-difluorobenzoate ##STR124## EXAMPLE 115##STR125## 4-(5-octyloxypyrimidin-2-yl)phenyl4-(4-cyclopropyl-butyloxy)-2,3-difluorobenzoate ##STR126## EXAMPLE 116##STR127## 4-(5-octyloxypyrimidin-2-yl)phenyl4-(4-cyclopropyl-butyloxy)-2,3-difluorobenzoate ##STR128## EXAMPLE 117##STR129## 4-(5-dodecylpyrimidin-2-yl)phenyl4-(4-cyclopropyl-butyloxy)-2,3-difluorobenzoate ##STR130## EXAMPLE 118##STR131## 2- (4-octyloxyphenyl)pyrimidin-5-yl4-(4-cyclopropyl-butyloxy)-2,3-difluorobenzoate ##STR132## EXAMPLE 119##STR133## 4- (2-octyloxypyrimidin-5-yl)phenyl4-(4-cyclopropyl-butyloxy)-2,3-difluorobenzoate ##STR134## EXAMPLE 120##STR135## 4-(2-octylthiopyrimidin-5-yl)phenyl4-(4-cyclopropyl-butyloxy)-2,3-difluorobenzoate ##STR136## EXAMPLE 121##STR137## 4-(5-octylpyridin-2-yl)phenyl4-(4-cyclopropylbutyloxy)-2,3-difluorobenzoate ##STR138## EXAMPLE 122##STR139## 4-(5-octylpyrimidin-2-yl)phenyl4-(8-cyclopropyl-octyloxy)-2,3-difluorobenzoate ##STR140## EXAMPLE 123##STR141## 4-(5-octyloxypyrimidin-2-yl)phenyl4-(8-cyclopropyl-octyloxy)-2,3-difluorobenzoate ##STR142## EXAMPLE 124##STR143## 2-(4-octyloxyphenyl)pyrimidin-5-yl4-(8-cyclopropyl-octyloxy)-2,3-difluorobenzoate ##STR144## EXAMPLE 125##STR145## 9-cyclopropylnonyl 4-(4-octyloxybenzoyloxy)phenyl ether##STR146## EXAMPLE 126 ##STR147## 9-Cyclopropylnonyl4-(4-octyloxybenzyloxy)benzoate ##STR148## EXAMPLE 127 ##STR149##7-Cyclopropylheptyloxy [4'-(4-octyloxybenzoyloxy)biphenyl-4-yl]##STR150## EXAMPLE 128 ##STR151##4,4'-Bis(7-cyclopropylheptyloxy)-1,1'-biphenyl ##STR152## EXAMPLE 129##STR153##trans-4-(cyclopropylmethyl)oxycyclohexyl-trans-4-propyl-cyclohexane##STR154## Extrapolated clear point ˜5° C. EXAMPLE 130 ##STR155##trans-4-(4-cyclopropylbutyl)oxycyclohexyl-trans-4-propyl-cyclohexane##STR156## Extrapolated clear point ˜5° C. EXAMPLE 131 ##STR157##5-Cyclooropylmethyloxy-2-(4-trifluoromethoxyphenyl)pyrimidine ##STR158##The clear point extrapolated from a mixture is 5° C. EXAMPLE 132##STR159##5-(4-Cyclopropylbutyl)oxy-2-(4-trifluoromethoxyphenyl)pyrimidine##STR160## The clear point extrapolated from a mixtures is 25° C.EXAMPLE 133

A binary mixture comprising:

65 mol-% of (4-hexyloxy)phenyl 4-octyloxybenzoate and 35 mol-% of(4-octyloxy)phenyl 4-(8-cyclopropyloctyloxy)-2,3-difluorobenzoate(Example 113) exhibited the following phase sequence:

    ______________________________________                                        Phases: X 34 S.sub.c 63 N 76 I                                                Comparison mixture:                                                           (4-Hexyloxy)phenyl 4-octyloxybenzoate                                                                65 mol %                                               (4-octyloxy)phenyl 4-decyloxy-2,3-                                                                   35 mol %                                               difluorobenzoate                                                              Phases: X 37 S.sub.c 69 N 81 I                                                ______________________________________                                    

Comparison of the mixture shows that the mixture according to theinvention had a melting point which was lower than that of thecomparison mixture. The cyclopropyl component is therefore particularlysuitable for practical application.

Having thus described in detail preferred embodiments of the presentinvention, it is to be understood that the invention defined by theappended claims is not to be limited by particular details set forth inthe above description as many apparent variations thereof are possiblewithout departing from the spirit or scope thereof.

What is claimed is:
 1. A liquid-crystallinecyclopropylalkyl-heterocyclic compound of the formula (I) ##STR161## inwhich R¹ is straight-chain or branched (with or without an asymmetricalcarbon atom) alkyl having 2 to 16 carbon atoms, it also being possiblefor one or two non-adjacent --CH₂ -- groups to be replaced by --O--,--S--, --CO--O-- or --O--CO--, or R¹ is one of the following radicals##STR162## A¹, A² and A³ are identical or different 1,4-phenylene,trans-1,4-cyclohexylene, pyridazine-3,6-diyl, pyridine-2,5-diyl,pyrimidine-2,5-diyl or (1,3,4)-thiadiazole-2,5-diyl,M¹ and M² areidentical or different CO--O, O--CO, CH₂ --O or O--CH₂, G isstraight-chain or branched alkylene having 1 to 16 carbon atoms, inwhich it is also possible for one or two non-adjacent --CH₂ -- groups tobe replaced by --O--, --O--CO-- or --CO--O--, R² and R³ are H orstraight-chain or branched alkyl having 1 to 16 carbon atoms and j, k, l, m and n are zero or 1, with the following provisos: a) j+l+n=2 or 3,and b) one of the groups A¹, A² and A³ is not 1,4-phenylene ortrans-1,4-cyclohexylene.
 2. A liquid-crystallinecyclopropylalkyl-heterocyclic compound as claimed in claim 1, wherein,in the formula (I) , the (--A¹)_(j) (--M¹)_(k) (--A²)_(l) (--M²)_(m)(--A³)_(n) -- group is ##STR163##
 3. A nematic liquid-crystallinemixture containing at least one cyclopropylalkyl heterocyclic compoundof the formula (I) as claimed in claim
 1. 4. A nematicliquid-crystalline mixture containing at least one cyclopropylalkylheterocyclic compound of the formula (I) as claimed in claim
 2. 5. Asmectic liquid-crystalline mixture containing at least onecyclopropylalkyl heterocyclic compound of the formula (I) as claimed inclaim
 1. 6. A smectic liquid-crystalline mixture containing at least onecyclopropylalkyl heterocyclic compound of the formula (I) as claimed inclaim
 2. 7. An electro-optical component containing a liquid-crystallinemixture as claimed in claim
 3. 8. An electro-optical component contininga liquid-crystalline mixture as claimed in claim
 4. 9. Anelectro-optical component contining a liquid-crystalline mixture asclaimed in claim
 5. 10. An electro-optical component contining aliquid-crystalline mixture as claimed in claim
 6. 11.5-(7-Cyclopropyl-heptyloxy)-2-pyrimidine.
 12. A cyclopropylalkylcompound of the general formula (I) ##STR164## in which R¹ isstraight-chain or branched (with or without an asymmetric carbon atom)alkyl or alkenyl having 2 to 16 carbon atoms, it also being possible forone or two non-adjacent --CH₂ -- groups to be replaced by --O--, --S--,--CO--, --CO--O--, --O--CO-- or --O--CO--O-- and it also being possiblefor H to be replaced by F, or is one of the following radicals##STR165## CN, OCF₃, OCF₂ H, F or CH₃ A¹, A² and A³ are identical ordifferent, unsubstituted or mono-or dihalo-substituted 1,4-phenylene,unsubstituted or 1- or 4-CN-substituted 1,4-cyclohexylene,pyridazine-3,6-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl or(1,3,4,)-thiadiazole-2,5-diylM¹ and M² are identical or different CO--O,O--CO, CH₂ --O, O--CH₂, C═C, CH₂ --CH₂ or a single bond G is astraight-chain or branched alkylene having 1 to 16 carbon atoms in whichit is also possible for one or two non-adjacent --CH₂ -- groups to bereplaced by --O--, --O--CO--, --CO--O--, R², R³ and R⁴ are H orstraight-chain or branched alkyl having 1 to 16 carbon atoms k and m arezero or 1 and j, l and n are zero, 1 or 2; and j+l+n is 2 or
 3. 13. Anembodiment as claimed in claim 12 wherein in the general formula (I),A¹, A² and A³ have the following meaning:A¹, A² and A³ are identical ordifferent mono-or difluoro-substituted 1,4-phenylene, unsubstituted1,4-phenylene, 1,4-cyclohexylene, pyridine-2,5-diyl orpyrimidine-2,5-diyl.
 14. A liquid-crystalline mixture containig at leastone cyclopropylalkyl compound of the general formula (I) as claimed inclaim
 12. 15. An electrooptical component containing aliquid-crystalline mixture as claimed in claim
 14. 16. Aliquid-crystalline mixture as claimed in claim 15, wherein theliquid-crystalline mixture is nematic.
 17. A liquid-crystalline mixtureas claimed in claim 15, wherein the liquid-crystalline mixture issmectic.
 18. A liquid-crystalline mixture as claimed in claim 15,wherein the liquid-crystalline mixture is chiral and smectic.
 19. Aliquid-crystalline mixture as claimed in claim 15, wherein theliquid-crystalline mixture is ferrolelectric.